The background art is characterized by vehicle propulsion mechanisms such as internal combustion engines, which convert the chemical energy contained in fuels to increase the pressure and temperature of a gas, forcing it to perform an expansion cycle which transforms this energy into the mechanical energy then used to power the vehicle, which in turn stores that energy as kinetic energy in its own movement.
This procedure is technically known as thermodynamic cycle. There are several thermodynamic cycles depending on their operating characteristics, including the Otto cycle, the Diesel cycle and the Rankine cycle.
A key feature of internal combustion engines is that they are unable to convert all the chemical energy stored in the fuel, since they transfer some of their heat to a cold source, as described by the laws of thermodynamics. The maximum theoretical efficiency of a thermodynamic cycle is determined by an ideal cycle called the Carnot cycle.
The other main feature of these engines is that they are based on thermal cycles, which involve irreversible physicochemical processes. This means that the engine cannot be turned into a generator and take mechanical energy to produce the chemical energy contained in a fuel.
Besides, most vehicle braking processes use an external device based on friction; thus, kinetic energy ends up being dissipated as heat.
The loss of energy in both the thermodynamic cycle and the braking process has been a permanent concern and has motivated the search for procedures, devices and innovations aiming to optimize fuel consumption in combustion engine vehicles.
One of the lines of research has focused on trying to recover a large portion of the kinetic energy dissipated in the brakes and use it again to accelerate the vehicle. The devices based on this concept have been classified under the acronym KERS, Kinetic Energy Recovery Systems.
Typically, KERS devices allow reducing the speed of a vehicle, turning a portion of its kinetic energy into another type of energy.
While they are mainly used in vehicles powered by electric energy—i.e. trains and subways—they are being used lately in hybrid vehicles, fitted with an internal combustion engine as well as an electric motor generator.
These KERS devices are also known as regenerative braking systems. For electric railways, they are used to feed their own power supply. For battery vehicles and hybrid vehicles, the energy is stored in a battery bank or a condenser bank for subsequent use.
Regenerative braking refers to a type of dynamic braking. Dynamic braking includes processes such as rheostatic braking, by which the electric energy generated by braking is dissipated as heat.
Regenerative brakes are based on the principle that an electric motor can be used as a generator. The electric traction motor is reconnected as a generator during braking and the power terminals are used to supply energy, which is fed into an electrical charge and this charge provides the braking effect.
When an electric train brakes, the traction motor connections are modified via an electronic device that works as an electric generator. For example, brushless DC motors typically have Hall effect sensors to determine rotor position, which provides information on the vehicle and enable calculations on how to feed the current generated in the motor into storage systems, which can consist of batteries or supercapacitors.
Motor fields are connected to the main traction motor and the armatures of the motor are connected to the load. The traction motor excites the motor fields, the wheels of the vehicle—those of a car, a trolley or a locomotive—turn the armature of the motor and the motor will act as a generator. When a motor is acting as a generator, the electrical energy produced by it can be fed through electric resistors, a process called rheostatic braking. If current is sent to the supply line in the case of a trolley or a locomotive, it can be conducted to a battery or a supercapacitor; in the case of an autonomous vehicle with a separate power line, this can be called regenerative braking.
If the movement of the vehicle is decelerated, the current flow through the armature of the motor upon braking must be opposite to that of the current used to drive the motor.
Braking effort is proportional to the product of magnetic strength of the field lines multiplied by the angular frequency of the armature.
For example, document US2002174798 describes a hybrid energy locomotive system having energy storage and a regeneration system. In one form, the system can be either retrofitted into existing locomotives or installed as original equipment in new vehicles. The energy storage and regeneration system captures dynamic braking energy, excess motor energy and externally supplied energy, and stores the energy in one or more energy storage subsystems, including a flywheel, a battery, an ultra-capacitor or a combination of such subsystems. The energy storage and regeneration system can be located in a separate energy tender vehicle. The separate energy tender vehicle is optionally equipped with traction motors. An energy management system is responsive to power storage and power transfer parameters, including data indicative of present and future track profile information, to determine present and future electrical energy storage and supply requirements. The energy management system controls the storage and regeneration of energy accordingly.
Electric regenerative brakes are also used in cars. An early example of this system was the regenerative brake developed in 1967 for the American Motors Corporation's Amitron and Gulton Industries. This car was completely powered by prototype-phase batteries, which were recharged by regenerative braking, resulting in an increase of the vehicle performance.
An alternative system to recover kinetic energy during braking is the flywheel. This component receives energy which would otherwise be dissipated as heat during braking, storing the recovered energy in a flywheel. This system was first used in the regulations for the 2009 Formula One season. Besides reducing costs, this device was designed to increase the number of overtakes during races and to make overtakes easier for the drivers. The system was designed and developed by Xtrac, Torotrack y Flybrid System, as per specifications set forth by the Fédération Internationale de L'Automobile (International Automobile Federation) and the European Union (EU).
Although not widely used, its use was later extended to regular cars. For instance, Toyota has been selling a hybrid model since 2010, the Auris HSD, which includes the regenerative braking system, among other improvements. Since 2007, BMW has been selling some serial models with Diesel and gasoline engines, under the Efficient Dynamics line with various improvements, including a Brake Energy Regeneration system. Currently, this system is used to recharge the battery of the vehicle without constantly using an alternator to charge the battery, either saving fuel or gaining power.
Volvo Car Corporation, a Swedish automobile manufacturer, has also developed in collaboration with Volvo Powertrain and SKF, a new KERS technology that can reduce fuel consumption by up to 25 percent, while enhancing engine performance in regular cars.
The system uses a flywheel to recover the kinetic energy lost during braking. When the car decelerates, the momentum of the car spins up the flywheel to 60,000 rpm. When the car starts off, the rotational force of the flywheel is transmitted to the rear wheels through a specifically designed transmission.
The combustion engine that drives the front wheels is switched off as soon as braking begins. The flywheel energy can be used to accelerate the vehicle when moving off again or to power the vehicle once it reaches cruising speed. Since the flywheel is activated by braking and the energy can be stored for a limited time, this technology is at its most effective during driving featuring repeated stops and starts. To put it differently, fuel efficiency is greater when driving in a heavy traffic city, and also during active driving.
The basic principles of this system can be found, for instance, in the document WO2012123710A1, which describes a high speed flywheel system for a vehicle capable of running at speeds of 20,000 rpm or greater, comprising: a flywheel mounted on a shaft and contained within a housing, and at least one bearing arrangement, where the bearing arrangement is mounted to the flywheel or the housing via an elastomeric component such as a ring and/or a metalastic bush to reduce Boise, vibration and harshness (NVH) and prevent the resonant modes of the flywheel and housing interfering with one another.
On the other hand, publication WO2011080512A1 describes an energy storage and recovery system device for a vehicle, comprising a flywheel, a first and a second set of gears and multiple wet multiplate clutches, wherein one of each gear set is arranged coaxially along a clutch shaft with one of the clutches, and wherein the device is coupled to the vehicle transmission, such that actuation of a clutch redirects the torque path via the gears, thereby enabling multiple rations and therefore, multiple speeds.
However, to this date there are no devices that transform the kinetic energy of a vehicle recovered from braking into fuel for its subsequent use in the same vehicle.
Therefore, it is necessary to improve existing processes or systems to obtain fuel from kinetic energy, thereby reducing fuel consumption in general, decreasing environmental pollution and helping to fight global warming. Besides, usage of equipment without moving parts instead of mechanical components can significantly reduce investment and maintenance costs.
Therefore, and in order to provide alternatives that can be used to help solving this long-standing problem, it would be desirable to promote systems that recover the kinetic energy of a vehicle dissipated during braking, while improving fuel consumption throughout the whole cycle.
For this purpose, the vehicles considered were those powered by Diesel engines with a four-stroke combustion cycle, such as those mounted on large-sized vehicles, with a Jake Brake. In this regards, U.S. Pat. No. 3,220,392 is herein cited and entirely incorporated by reference. This patent was granted on Nov. 30, 1965, to C. L. Cummins, and discloses this type of braking system.